Characterization of large-EPCs or small-EPCs. (a) Proliferation assay of large-EPCs or small-EPCs from peripheral blood mononuclear cells (PB-MNCs) (upper) or bone marrow mononuclear cells (BM-MNCs) (bottom). After 7 days of culture, large-EPC-CFUs or small-EPC-CFUs were allowed to incorporate bromodeoxyuridine (BrdU) for 24 hours and analyzed by flow cytometry. Large-EPCs had significantly lower proliferative potency than small-EPCs in both PB-MNCs and BM-MNCs (*P < 0.05 versus large-EPCs). (b) Adhesion assay of large-EPCs or small-EPCs from PB-MNCs or BM-MNCs. Large-EPCs (white columns) or small-EPCs (black columns) were allowed to adhere to a fibronectin-coated plate for 20 minutes. More large-EPCs had adhesive capacity than small-EPCs. *P < 0.05, **P < 0.01 versus small-EPCs. (c) Tubular formation assay of large-EPCs or small-EPCs from BM-MNCs. Large-EPCs or small-EPCs labeled with 1,1'-dioctadecyl-3,3,3',3-tetramethyl-indocarbocyanine perchlorate-labeled acetylated-low density lipoprotein (acLDL-DiI) (red) were cocultured with endothelial cells (ECs) to form tubular structures within Matrigel. Representative light and fluorescent micrographs of ECs cocultured with large-EPCs (upper) and small-EPCs (bottom) are shown. Scale bar represents 500 μm. (d) Quantification of the number of tubes (left). Large-EPCs made a substantial contribution to tubular networks with ECs. *P < 0.05 versus small-EPCs. (d) Quantification of the number of cells incorporated into tubes (right). Small-EPCs showed minimal incorporation into the developing vascular network. **P < 0.01 versus small-EPCs. EPC, endothelial progenitor cell.